Refrigeration machine

ABSTRACT

A refrigeration machine, in particular a cryopump for generating a vacuum, having a compressor for compressing a refrigerant substantially comprising helium and oil. Together with the compressor, an oil separator is arranged downstream in the delivery direction of the coolant. Furthermore, a cooling device in which the refrigeration medium expands. In order to adsorb harmful gases, an adsorption device is arranged upstream of the cooling device in the delivery direction.

BACKGROUND 1. Field of the Disclosure

The disclosure relates to a refrigeration machine, in particular to a cryopump for generating a vacuum.

2. Discussion of the Background Art

With the use of refrigeration machines, which find application, among others, in cryopumps, it is possible to obtain very low temperatures of less than 10 K. Thereby, it is possible e.g. to generate a very high vacuum of up to 10⁻¹⁰ mbar in a closed vacuum chamber. Refrigeration systems comprise a compressor pump, such as e.g. a scroll pump, with which a refrigerant is compressed. Helium is used as the refrigerant. The same generally comprises a certain proportion of oil to prevent excessive heating of the helium during compression. A heat exchanger is arranged first downstream of the compressor, seen in the delivery direction of the refrigerant, so as to allow for a cooling of the medium. Thereafter, the oil present in the helium is separated. This is effected, for example, by providing a plurality of oil separators, in particular at least one pre-separator and at least one fine separator. Further, the oil separator typically comprises an adsorber to filter out oil vapors and the like. Behind the adsorber, the refrigerant is substantially clean so that, to an extremely high extent, it consists of only helium. The proportion of oil is in the ppb range.

Occasionally, problems occur in refrigeration machines already after relatively short operating periods. Sometimes, it is no longer possible already after short operating periods to cool down the cooling device, such as the cold head, to the lowest temperature. It is therefore necessary to maintain and clean the cold head on a regular basis to be able to generate the desired low temperatures. This entails high costs.

It is an object of the disclosure to provide a refrigeration machine for which the maintenance intervals can be extended.

SUMMARY

The refrigeration machine of the disclosure serves to generate low temperatures in the cooling device of in particular less than 10 K. Suitable refrigeration machines for this purpose are the applicant's machines of the Coolpower series, for example. The refrigeration machine comprises a compressor compressing the refrigerant. An oil separator, which may possibly comprise a plurality of in particular successive oil separators, is arranged downstream of the compressor in the delivery direction of the refrigerant. In particular, the oil separator may comprise a coarse and/or a pre-separator and in particular a plurality of fine separators. It is further preferred that the oil separator comprises an oil adsorber for cleaning the refrigerant. Further, a heat exchanger may be provided between the compressor and the oil separator. Moreover, the refrigeration machine comprises a cooling device, such as a cold head. The refrigerant expands in the cooling device.

Studies have shown that the present hypotheses on why a cryopump can no longer cool down to the desired low temperatures are not entirely correct. Up to the present it has been assumed that that traces of oil and/or water still present in the refrigerant even after cleaning are responsible for the necessity of frequent maintenance work on the cooling device and the cold head, respectively. Studies have now shown that the impairment of the cooling device is particularly due to the presence of nitrogen and oxygen. Other gases such as neon, argon, carbon dioxide or the like may also have adverse effects if they occur.

Therefore, according to the disclosure, a gas adsorption device is arranged upstream of the cooling device in the delivery direction. At least a part of the detrimental gases is filtered from the refrigerant by the gas adsorption device. As a consequence, these gases, which freeze in the cooling device, are no longer present and the required maintenance intervals can thus be extended.

The gas adsorption device is preferably configured such that detrimental gases are adsorbed which freeze in particular at temperatures of less than 150 K, particularly preferred less than 120 K and in particular less than 70 K. Of course, helium is not adsorbed.

The gas adsorption device preferably filters and/or adsorbs nitrogen and/or oxygen. Preferably, other gases that can freeze in the cold head, such as neon, argon or carbon dioxide, are also filtered or adsorbed, respectively.

In a particularly preferred embodiment, the gas adsorption device is arranged in a range in which a freezing of the corresponding detrimental gases can not yet occur. Preferably, the gas adsorption device is thus arranged in a range>150 K, preferably a range between 150 K and 300 K. Here, the gas adsorption device may be arranged outside and upstream of the cooling device. Likewise, it is possible to arrange the gas adsorption device e.g. at the inlet of the cooling device.

It is particularly preferred that the gas adsorption device is arranged downstream of the oil separator in the flow direction of the refrigerant. In particular, the gas adsorption device is arranged downstream of an oil adsorber of the oil separator device so that no contamination of the gas adsorption device by oil can occur.

This gas adsorption device may be configured as an adsorbing layer and/or powder and/or fabric and/or screen. A suitable adsorbing material is zeolite, for example. This is described e.g. in DE 69606117.

Further, the disclosure relates to a use of a gas adsorption device in the coolant circuit of a refrigeration machine. Here, the gas adsorption device is used, in particular the above described preferred embodiments of the gas adsorption device. Specifically, the gas adsorption device used comprises the characteristics described above with reference to the cryopump.

The disclosure will be explained in more detail hereinafter with reference to a preferred embodiment and to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows a schematic structure of a cryopump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The cryopump comprises a compressor 10 which in the embodiment illustrated is a scroll pump. The compressor 10 is supplied with helium via a line 12 and with oil via a line 14. This compressed mixture of helium and oil which serves as a refrigerant, is conveyed to a heat exchanger 18 via a line 16. There, the refrigerant heated by compression is cooled. Thereafter, the oil is filtered from the refrigerant. An oil separator is provided for this purpose. In the embodiment illustrated the oil separator comprises a pre-separator 20, a first fine separator 22, a second fine separator 24 and an adsorber 26.

A pressure relief valve 27 provided between high and low pressure is arranged between the second fine separator 24 and the adsorber 26.

In the embodiment illustrated, the gas adsorber device 28 is arranged downstream of the adsorber in the delivery direction. The former is thus arranged upstream of the cooling device 30 or the cold head in the flow direction.

The gas adsorption device 28 is arranged in a region upstream of the cooling device 30 in which the temperature is higher than the temperature at which the gas to be adsorbed freezes.

The refrigerant expanded in the cooling device returns to the compressor 10 via a line 32 and the line 12. Likewise, the separated oil is returned via lines 34, 36, 38. 

What is claimed is:
 1. Refrigeration machine, in particular a cryopump for generating a vacuum, having a compressor for compressing a refrigerant substantially comprising helium and oil, an oil separator arranged downstream of the compressor in the delivery direction of the refrigerant and a cooling device in which the refrigerant expands, wherein a gas adsorption device is arranged upstream of the cooling device in the delivery direction.
 2. Refrigeration machine of claim 1, wherein the gas adsorption device adsorbs detrimental gases that freeze at temperatures of <150 K.
 3. Refrigeration machine of claim 1, wherein the gas adsorption device is configured to filter nitrogen and/or oxygen.
 4. Refrigeration machine of claim 1, wherein the gas adsorption device is arranged in a region upstream of the cooling device, where the temperature is higher than the temperature at which the gas to be absorbed freezes.
 5. Refrigeration machine of claim 1, wherein the gas adsorption device is arranged downstream of the oil separator in the delivery direction.
 6. Refrigeration machine of claim 1, wherein the gas adsorption device is arranged in the cooling device in particular in the inlet region of the cooling device.
 7. Refrigeration machine of claim 1, wherein the gas adsorption device is configured as an adsorbing laxer and/or powder and/or fabric and/or screen.
 8. A method of using a gas adsorption device in a coolant circuit of the refrigeration machine according to claim
 1. 9. Refrigeration machine of claim 1, wherein the gas adsorption device adsorbs detrimental gases that freeze at temperatures of <120 K.
 10. Refrigeration machine of claim 1, wherein the gas adsorption device adsorbs detrimental gases that freeze at temperatures of <70 K. 